Specimen Collection

Sample stability:

• 7 days at 15-25 ^o C
• 3 weeks at 2-8 ^o C
• 8 months at -20 ^o C

4.5 mL PST Blood (Preferred)

0.5 mL Paediatric Micro-PST Blood (Preferred)

5 mL Heparin Blood

4 mL Plain Blood

3.5 mL SST Blood

0.5 mL Microsample Blood

0.5 mL Paediatric Micro-heparin Blood
Reference Intervals

Units: mmol/L

Age: Day 1 to 3	1.80 - 2.80
Day 4 to 1yr	2.10 - 2.80
>1yr:	2.10 - 2.55

This test measures total plasma calcium (includes ionised, protein-bound, and complexed fractions).

Reference ranges above apply to total calcium when serum albumin is normal , and to corrected calcium (adjusted for albumin concentration).

Serum albumin should always be measured in conjunction with total calcium, to enable calculation of corrected calcium.

Prolonged stasis during venepuncture and haemolysis will give falsely high values.

Conversion factors:

mg/100 mL x 0.25 = mmol/L

mmol/L x 4 = mg/100 mL

Uncertainty of Measurement: 5%

Turnaround Time: Within 3 hours
Assay Method

Principle : Colorimetric

Reagents: Roche CA2 kit

Analyser: Cobas c702

Diagnostic Use and Interpretation

Increased calcium concentrations: primary and tertiary hyperparathyroidism, malignancies (both with and without bone involvement), sarcoidosis, vitamin D overdosage, dehydration, Paget's disease (with immobilisation) and genetic disorders of the calcium sensing receptor.

Decreased calcium concentrations: hypoparathyroidism, pseudohypoparathyroidism, chronic renal failure, renal tubular disorders, magnesium deficiency, vitamin D deficiency, prolonged anticonvulsant therapy, acute pancreatitis, rickets and osteomalacia.

Corrected or adjusted calcium

The routine test for plasma calcium concentration measures the total calcium (bound plus ionised calcium ). Approximately 50% of plasma calcium is bound to albumin, and this bound fraction is biologically inactive. Therefore changes in albumin concentration will affect the total calcium concentration without affecting the ionised (active) fraction of plasma calcium.

In order to allow the use of a single reference interval for total calcium, irrespective of albumin concentration, the total calcium can be adjusted using a formula. This is known as the "corrected" or "adjusted" calcium.

The formula used is:

[Ca adjusted] = [Ca total] + 0.012 x (39.9 - [albumin])

Reference

James M, Zhang J, Lyon A, Hemmelgarn B. Derivation and internal validation of an equation for albumin-adjusted calcium. BMC Clinical Pathology 2008;8:12.

Contact Information

The chemical pathology team can be reached via email: chemicalpathologist@adhb.govt.nz or via Lablink (09) 307 4949 ext 22000 or 09-3078995

Emails will receive priority attention from the on-call chemical pathologist. Include the patients NHI.

After-hours: contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours .

• Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
• Dr Cam Kyle : CampbellK@adhb.govt.nz ext 22052
• Dr Weldon Chiu : WeldonC@adhb.govt.nz ext. 23427
• Dr Campbell Heron : CHeron@adhb.govt.nz ext. 23427
• Dr Sakunthala Jayasinghe Saku.Jayasinghe@adhb.govt.nz
• Dr Owen Yi WenyiYi@adhb.govt.nz

Last updated at 11:42:03 16/01/2026